The ability to distribute limited mental resources among tasks or stimuli and to efficiently shift the "internal spotlight" of attention among multiple representations in working memory is critical to adaptive functioning in a demanding and complicated world. The prefrontal regions of the human brain that have been implicated in volition, cognitive control, and working memory are thought to be critical to attentional multiplexing, and many neurological and neuropsychiatric conditions that are associated with frontal pathology are often accompanied by impairments in it. Current static tests of the "frontal executive system" derived from traditional paper and pencil neuropsychological or psychometric techniques do not test the rapid dynamics of attentional multiplexing, are not designed for repeated administration, and are not easily adapted for concurrent acquisition of physiological measurements of brain function. This project aims to develop a specialized, dynamic, computerized stress test that will overcome these limitations. As a basic research tool the Attentional Multiplexing Test (AMT) could serve as a standardized activation procedure for neuroimaging studies aimed at clarifying the neural basis of the executive attention system. As a clinical test the AMT could both aid in the assessment of patients with executive function abnormalities, and serve as an outcome measure in treatment efforts to ameliorate their cognitive impairments. The Phase I effort will leverage our experience with measuring brain function and behavior during tasks that stress executive functions, and builds on an early prototype of the task that has been tested in healthy young adults. In Phase I the AMT will be refined for use across the lifespan, re-engineered to permit simultaneous neurophysiological data collection, and initially evaluated in a small experiment that will test its stability, reliability, sensitivity to frontal lobe dysfunction, and neural correlates. In Phase II larger studies would evaluate its construct and discriminant validity, and further characterize the neurophysiological and neuroanatomical correlates of its performance. It would then be provided to collaborating laboratories for independent evaluation. [unreadable] [unreadable]